I ask because, provided I live that long, this year I turn 65, the age which I traditionally associated with "Senior Citizen." I never had grandparents to interact with, so I guess the default retirememnt age became my default geezer age.
I think AARP starts accepting members at age 50.
Over the past decade or so, I've become more and more comfortable about asking if there's a senior citizen discount. My mentor at the muffler and brake shop would be proud of me.